#include <cstdio>
#include <stdio.h>
#include <stdbool.h>
#include <iostream>
#include <map>
#include <vector>
#include <climits>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cmath>
#include <cctype>
#include <bitset>
#include <iomanip>
#include <cstring>
#include <numeric>
#include <cassert>
using namespace std;
#define int long long
#define pii pair<int, int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, m, k, sum=0, a, sum2=0;
cin>>n>>m>>k;
for (int i=0; i<n; ++i){
cin>>a;
if (a<k){
cout<<"impossible";
return 0;
}
sum+=a;
}
vector<int> dp(90005, LLONG_MIN/2);
dp[0]=0;
while (m--){
cin>>a;
sum2+=a;
for (int i=sum2; i>=a; --i)dp[i]=max(dp[i], dp[i-a]+min(a, n));
}
for (int i=sum; i<=sum2; ++i)if (dp[i]>=n*k){
cout<<i-sum;
return 0;
}
cout<<"impossible";
}
